Global gitignore - how to exclude a single specific folder

Question

I would like to exclude all .idea files in a specific folder through a global .gitignore (located in ~/.gitignore_global).

I tried to put a following lines there:

# assuming .gitignore_global understands absolute paths
/Users/<my home folder>/Desktop/Dev/**/.idea

# assuming .gitignore_global takes a location of global gitignore (~) as a root
Desktop/Dev/**/.idea

Neither seem to work (however, adding just .idea works, so this global gitignore is used by git - however, I don't want to ignore .idea for my personal projects in other folders).

How are global excludes supposed to work?

Which folder is considered by git as a 'root'? (in case of normal .gitignore, all paths are relative to a repository root, but global gitignore seems to work differently).

Thanks!

I'm on a Mac, git version 2.17.2 (Apple Git-113)

EDIT: As per @torek:

The global gitignore is treated as if it were in the root Git directory (the work-tree top level).

So, there is no way to accomplish this, as there is no way to check the path of a whole project.

Answer 1

It's actually possible with this workaround with these files:

~/.gitconfig

[includeIf "gitdir:~/my-specific-repo/"]
  path = ~/tailored-gitconfig/my-specific-repo/gitconfig

~/tailored-gitconfig/my-specific-repo/gitconfig

[core]
  excludesFile = ~/tailored-gitconfig/my-specific-repo/gitignore

~/tailored-gitconfig/my-specific-repo/gitignore

file-to-ignore
folder-to-ignore

In this way, "global" gitignore kicks off only within certain path.

~/tailored-gitconfig is an arbitrary path for the example.

Answer 2

As per @torek in comments:

The global gitignore is treated as if it were in the root Git directory (the work-tree top level).

So, there is no way to accomplish this, as there is no way to check the path of a whole project.